Really? have you actually read these? http://www.fangraphs.com/library/misc/war/ "Given the nature of the calculation and potential measurement errors, WAR should be used as a guide for separating groups of players and not as a precise estimate." "Our measures of both are more uncertain than our measures of offense, so players who get a good amount of their value through their defensive ratings likely have more uncertainty around their WAR value than players who have defensive value closer to average. This does not mean that WAR is wrong or biased, but rather that it is not yet capable of perfect accuracy and should be used as such." http://www.fangraphs.com/blogs/the-fangraphs-uzr-primer/ because they admit, over and over, that they are estimating things and that it is not precise. They freely state exactly what they do to calculate the stat. If one can't figure out that it is based on observation and estimates of defense, then they aren't reading the definition and explanation at all. "So, even after regression, there is no guarantee that our UZR number reflects what the player actually did or his true defensive talent over that time period. But, it is the best we can do (not knowing anything else about that player)!" http://www.fangraphs.com/library/defense/drs/ "Before drawing any conclusions about a player’s defense, look at a full three years of defensive data, drop the decimal points and take an average, and compare DRS scores with other defensive metrics (UZR, TZL, etc.). By taking a broader picture, you will help ensure that you’re not being over-confident or overstating a player’s defensive abilities."